1. Field of the Invention
The present invention relates to an image communication apparatus, and more particularly to an image communication apparatus having a unity-magnification transmission/reduced size transmission function.
2. Related Background Art
A facsimile apparatus which transmits image data of a reduced size in accordance with a user setting or in order to match a size of a document sheet or record sheet at transmitting and receiving stations has been known. Such a facsimile apparatus having the reduced size transmission function is disclosed in U.S. Pat. Nos. 4,353,097; 4,423,439; 4,814,894; 4,772,955; 4,845,569 and 4,885,641.
In a convertional facsimile apparatus, a certain minimum time is required to read one line of image data. In a receiving station, a certain minimum time is also required to record the received one line of image data. Accordingly, in the facsimile transmission, if the time required to transmit one line of image data is shorter than the minimum read time (a minimum transmission time of the transmitter) or the minimum record time (a minimum transmission time of the receiver), the image data to be transmitted may be empty or the data may overflow at the receiving station. Thus, the longer one of the minimum transmission time of the transmitter and the minimum transmission time of the receiver is set as a minimum transmission time of the communication. If the time required to transmit one line of image data is shorter than the preset minimum transmission time, fill data is added to the line data before the transmission. The addition of the fill data is disclosed in U.S. Pat. Nos. 4,719,514 and 4,775,893.
The minimum transmission time of the transmitter is determined by a storage time of a read device such as CCD and a feed speed of a feed motor for the document sheet. In the facsimile apparatus having the reduced size transmission function, a single minimum transmission time for the transmitter is set whether it is used in a unity-magnification transmission mode or a reduced size transmission mode. Since the transmission is done with the single minimum transmission time for both the unity-magnification transmission mode and the reduced size transmission mode in the prior art apparatus, it is necessary to rotate the document sheet feed motor faster in the reduced size transmission mode than in the unity-magnification mode. Thus, a high performance motor is required and this leads to the increase of a cost.
Instead of increasing the speed of the feed motor in the reduced size transmission mode, the minimum transmission time of the apparatus may be set to fit to the reduced size transmission mode. In this case, however, the minimum transmission time is long in the unity-magnification transmission mode and a longer transmission time is required.